Satellite receivers are installed in moving objects, such as vehicles, ships, trains, or the like, to automatically track the position of an artificial satellite such that viewers can watch satellite broadcasting without adjusting a satellite antenna. The satellite receiver includes a satellite antenna, an exclusive tuner, and a monitor. An antenna body is installed with a device for adjusting azimuth angle and elevation angle of the satellite antenna such that the position of the satellite is automatically tracked without adjustment of the wave-receiving angle of the satellite antenna.
As for an elevation angle control apparatus of a satellite-tracking antenna related to the present invention, a gear type elevation angle control apparatus, a linear motor type elevation angle control apparatus, and a belt type elevation angle control apparatus are generally used.
The three elevation angle control apparatuses will be described in brief. First, the gear type elevation angle control apparatus, as disclosed in U.S. Pat. No. 4,887,091 granted to Takahiro Yamada and U.S. Pat. No. 6,023,247 granted to Charles Eugene Rodeffer, has a simple structure such that a geared motor coupled with an elevation angle shaft adjusts elevation angle of a frame for supporting an antenna but also has drawbacks such that adjustment of the elevation angle of the antenna is not stable because of backlash the antenna is vibrated by moment of inertia when adjusting elevation angle of the antenna. Moreover, since driving power is transmitted when gears of the geared motor are engaged with gears of the elevation angle shaft, minute and accurate adjustment of elevation angle of the antenna is restricted.
The linear motor type elevation angle control apparatus, as disclosed in U.S. Pat. No. 5,528,250 granted to William J. Sherwood, has a structure wherein a shaft of a linear motor is directly and pivotally coupled to a location spaced apart from an elevation angle shaft of a frame for supporting an antenna, or a separate link mechanism is disposed between a supporting bracket and a frame and the shaft of the linear motor is coupled with a side of the link mechanism to expand and contract the shaft of the linear motor. The linear motor type elevation angle control apparatus adjusts elevation angle of the satellite antenna by pushing and pulling the link mechanism. Although, since a point to which force for adjusting elevation angles of the elevation angle shaft and the antenna is applied, is separated, the backlash is reduced in comparison to the gear type elevation angle control apparatus, the backlash is still generated in the linear motor type elevation angle control apparatus. In the linear motor type elevation angle control apparatus employing the separated link mechanism, its structure becomes complex, and additionally, control for the adjustment of minute elevation angle is difficult because of the shaft of the linear motor directly coupled with the frame or the link mechanism.
A typical belt type elevation angle control apparatus is disclosed in U.S. Pat. No. 6,188,367 granted to Stephan A. Morrison. According to Morrison's patent, belts are connected to both ends of a frame for supporting an antenna and are pulled to one side or the other by rotating a driving device forward and backward such that the frame is rotated on an elevation angle shaft. The belt type elevation angle control apparatus is advantageous to remove the backlash, shortcoming of the gear type elevation angle control apparatus and the linear motor type elevation angle control apparatus, by driving the belts to adjust angle of the frame. However, the belt type elevation angle control apparatus also has shortcomings that a large space on the lower part of both sides of the frame is required to install the belts. Since the belts are long, the slack of the belts brought by long term use causes inaccurate driving and devices for guiding the belts must be installed in front of and at the rear side of the supporting bracket. Since both ends of the frame are connected to the belts, the frame must be longer than unnecessarily and its volume is increased. Moreover, since the structure of the frame of a flat type satellite antenna where the antenna is installed is different from that of a parabolic satellite antenna, the belt type elevation angle control apparatus cannot be applied to the flat type satellite antenna.